What is Sumitomo SH220LC-5 Fault Code 601?

Fault Code 601 on the Sumitomo SH220LC-5 excavator indicates a malfunction in the engine pre-heating system, specifically related to the glow plug relay circuit or individual glow plug failure. This code is triggered when the Electronic Control Module (ECM) detects abnormal current flow, voltage irregularities, or open/short circuits within the glow plug system during the pre-heat cycle.

The glow plug system is critical for cold-start performance in diesel engines, particularly in the Isuzu engines commonly found in SH220LC-5 models. When this system fails, the combustion chamber temperature cannot reach optimal levels for ignition, leading to hard starting conditions, excessive white smoke, and potential engine damage from incomplete combustion. In used excavators, this code frequently appears due to aging electrical components and accumulated operational hours affecting relay contacts and glow plug integrity.

Common Symptoms

• Hard starting or no-start conditions, especially in cold weather or after the machine sits overnight
• Excessive white or gray smoke during initial startup that persists longer than normal
• Rough idle and engine misfiring for the first several minutes of operation until the engine reaches operating temperature
• Glow plug indicator light remains illuminated on the dashboard or flashes intermittently
• Extended cranking time required before the engine fires, putting excessive strain on the starter motor and battery

Potential Causes

The most common technical causes for Code 601 on used SH220LC-5 excavators include:

• Failed glow plugs due to carbon buildup, tip erosion, or internal element breakage (common after 3,000+ operating hours)
• Faulty glow plug relay with burned or pitted contacts preventing proper current delivery to the glow plug circuit
• Damaged wiring harness particularly at flex points near the engine valve cover where vibration causes wire insulation breakdown
• Corroded electrical connectors on individual glow plug terminals or the main harness connector, especially in machines operated in wet or marine environments
• Low battery voltage causing insufficient current flow during the pre-heat cycle, triggering false fault detection
• ECM internal relay failure or software calibration issues in older control modules

How to Troubleshoot and Fix Code 601

Step 1: Visual Inspection and Voltage Testing Begin by inspecting all glow plug wiring for visible damage, particularly where harnesses contact the engine block or valve cover. Check battery voltage with a multimeter—it should read 12.4V minimum with the engine off. Inspect the glow plug relay (typically located in the fuse/relay box) for signs of overheating or corrosion on terminals.

Step 2: Individual Glow Plug Resistance Testing Disconnect the electrical connector from each glow plug and measure resistance between the glow plug terminal and engine ground. Specification for most Isuzu engines in this model is 0.5-2.0 ohms. Any reading above 5 ohms or infinite resistance indicates a failed glow plug requiring replacement. On used excavators, it's recommended to replace all glow plugs simultaneously if one fails, as others are likely near end-of-life.

Step 3: Relay and Circuit Testing Using diagnostic software (Sumitomo-specific or compatible scan tool), activate the glow plug relay while measuring voltage at the glow plug bus bar. You should see 12V+ during the pre-heat cycle. If voltage is present at the relay but not at the glow plugs, inspect the main feed wire for breaks or high resistance connections. Test relay operation by listening for an audible click and measuring continuity across relay terminals during activation.

Step 4: Harness and Connector Inspection For used machines, pay special attention to connector corrosion at each glow plug. Remove connectors, clean terminals with electrical contact cleaner, and apply dielectric grease before reassembly. Check harness routing for areas where cable chafing against metal surfaces has compromised insulation—a common issue on high-hour SH220LC-5 excavators.

Step 5: Clear Code and Verify Repair After repairs, clear the fault code using diagnostic software and perform a cold-start test. Monitor the glow plug indicator light cycle time (should be 5-15 seconds depending on ambient temperature) and verify smooth engine starting with minimal smoke.

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Disclaimer: This guide provides general troubleshooting information for Sumitomo SH220LC-5 excavators. Always consult the manufacturer's service manual for model-specific procedures and specifications. If you're unfamiliar with electrical diagnostics or lack proper tools, consult a certified heavy equipment technician to prevent further damage or safety hazards.